I started with checking out the analytical models of the psfs to try to find one that fit well. I ran DAOphot using each option to check out the residuals. I compared the chi^2 DAOphot printed to the screen for each model. A good chi^2 is close to 0--it represents the percent deviation, root-mean-square, to which DAOphot's first approximation matches the observed stellar profiles, on average.
Model // Chi^2
Gaussian (#1) // 0.0224
Moffat, beta=1.5 (#2) // 0.0500
Moffat, beta=2.5 (#3) // 0.0197
Lorentz (#4) // 0.0137
Penny, 4 free (#5) // 0.0544
Penny, 5 free (#6) // 0.0136
Super Secret (#7) // 0.0134
Looks like the super secret model wins out, but the 5-free-parameter Penny and Lorentz models are close behind.
In an effort to address the distortion problems Dave brought up yesterday, I've created multi-extension fits (MEF) files similar to what he was using.
I'll scamp all 10 of the MEF files at once to see if I can get a distortion file that shows all 8 chips. If this works, I'll swarp the files to see if that looks good. If swarp looks good, I'll redo DAOphot and test the different analytical models once again just to be sure I've got the best one.
Assuming all of this runs smoothly, I'll also talk to Beth about CMD calibration, which we pushed back today when I got stuck with this mef stuff.